Sound reproducing and recording apparatus



R. G. MITCHELL.

SOUND REPRODUCING AND RECORDING APPARATUS.

APPLICATION FILED MAR.24. 19 9.

1,3 1 3,720. Patented Aug. 19, 1919.

INE/VTOR ROBERT G. MITCHELL,

0F MOUNT VERNON,

NEW YORK.

SOUND REPRODUCING AND RECORDING APPARATUS.

To all whom it may concern Be it known that I, .ltonnlrr (t, MITCHELL, a citizen of the l nited States of America, residing at Mount Vernon, New York, have invented a new and useful Sound Iteproducing and Recording Apparatus, of which the following is a specification.

My invention relates to sound reproducing and recording mechanism, and relates particularly to what is commonly termed a sound box, that is to say, a device arranged to be employed in connection with a phonograph or a talking machine for the reproduction of sounds which have been recorded in suitable records. In the present instance, I have illustrated my invention in connection with a sound box such as used with flat disk records containing a record groove therein, the undulations in the walls of which operate to move a needle bar which is associated with the sound box. The main object of my invention is to improve the quality of sound reproduced and to practically eliminate the hissing or scratching sound commonly caused by the scraping of the needle in the record groove.

In the accompzmying drawing. I have shown a sectional view of a sound box constructed to el'nbody my invention.

1 represents the main housing of the sound box which may have the usual extension 2 by which the sound box is connected to the usual horn, not shown. 3 is the sound reproducing diaphragm. 4 ]S a second diaphragm spaced apart from the diaphragm 3 and to which is connected a needle bar 5, which latter is pivoted to the housing 1, said needle bar serving as one well known means for transferring the vibrations of the record groove to the diaphragm 4.

Between the diaphragm 4 and the diaphragm 3 is a member or partition ll which in the present instance, is in the form of a substantially rigid disk having a central aperture 7. 8-8 are suitable packing washers for supporting the diaphragms, and if desired, for supporting the member 6. The clearance, as shown, between the diaphragm 4 and the member 6 is such that the said diaphragm 4 may be vibrated to its intended operative limit without danger of contact with the adjacent member 6. It is also apparent that the diaphragm 3 may vibrate to its intended operative limit. with out danger of contact with either the mem- Specification of Letters Patent.

Application filed March 24, 1919.

Patented Aug. 19, 1919.

Serial No. 284,764.

her 6 or the inner wall of the housin For convenience in assembling, the housing 1 may have detiachalbly secured thereto by any suitable means, a ring 9 which serves to-overstand the outer diaphragm and hold the several internal operative parts in place.

The operation of the sound box for the purpose of reproducing sound is as follows: \Vhen the needle bar 5 is vibrated by means of the record, it causes a correspond ing vibration of the diaphragm at. As the diaphragm 4 vibrates to and fro, the air contained between the two diaphragms 3 and t vibrates correspondingly to and fro through the passage 7 in the member 6, so that said air acts as a pneumatic coupling or link between the central portion of the diaphragm r and the central portion of the diaphragm 3, by means of which link the diaphragm 3 is vibrated in keeping with the vibrations of the diaphragm 4. The size of the opening 7 may be varied to some extent depending in some measure upon the thick ness and size of the diaphragms I and 3 respectively, but in all cases, it will be observed that the impact of the air or pneumatic coupling between the two diaphragms instead of being disposed generally over the diaphragm 3 as the diaphragm -l' is vibrated, is centralized with relation to diaphragm 3 so that the sound waves or vibrations in the latter are generated at the center and flow outwardly toward the edges of said reproducing diaphragm. I have found that by this means highly satisfactory results in tonal quality are attained without sacrifice of amplitude or detail. I have also found that by having the needle bar entirely free, mechanitailly speaking. from the reproducing diaphragm 3, the objectionable scratching sound commonly heard in the ordinary sound box, is practically eliminated.

\Vhile I have primarily described my invention as a means for reproducing sound, obviously, the apparatus may be effectively used for the purpose of recording sound in the same manner as any sound box would be used for the purpose of recording. I apprehend however that as a reproducing device the instrument is most highly successful. because one of my aims is to eliminate; or practically eliminate the objectionable sound produced by the scratching of the needle along the record, which in the re- )roduction of sound in the ordinary sound box is so highly magnified as to be distinctly objectionable; By my improved construc tion I find that Iv am able to successfully use diaphragms of substantially the same size, thickness and material. I also find that I am not limited to the selection of any particular material for the making of said diaphragms although of course it was pref" erable to select a material which is sufii- 'ciently flexible and yet firm enough to be responsive to vibration. While I have shown both diaphragms as of the same diameter, I do not wish to be understood as being limited thereto. Indeed, I wish it to be understood that I contemplate that substantial changes and modifications may be made in .the apparatus which is herein shown as a preferable form without departure from the spirit and scope of the invention.

\Vhat I claim is:

1. In a sound box, two spaced diaphragms,

a housing surrounding the diaphragms tially inclose the space between said diaphragms, a partition having a central passage therethrough located between said diaphragms.

3. In a sound box, two spaced diaphragms, a housing surrounding the same to substantially inclose the space between said dia- 'ihragms, a partition having a central passage therethrough located between said diaphragms, means for vibrating one of said diaphragms to cause pulsations of air 'to and fro through said passage.

4. Iii a sound box, a housing, two diaphragms mounted within the same and spaced apart from each other, with means carried by said housing for providing a pneun'iatie connection between the central parts of each of said diaph 'agms.

5. In a sound box, a housing having a relatively contracted outlet at its back, two diaphragms of greater diameter than said outlet mounted insaid housing, means between said diaphragn'is to cause pulsations of air created by'one of said diaphragms to be transmitted to the other diaphragm, said mea. comprising a substantially rigid partition perforated to provide an air passage.

ROBERT G. MITCHELL. 

